The present invention relates generally to hydromechanical limited slip couplings of the type used in motor vehicle driveline applications. In particular, the present invention is directed to a hydraulic coupling having a hydraulic pump, a transfer clutch, and a fluid distribution system for distributing fluid from the pump to a first chamber for actuating the transfer clutch and to a second chamber for lubricating and cooling the transfer clutch.
Hydraulic couplings are used in various vehicular drivetrain applications to limit slip and transfer drive torque between a pair of rotary members. In all wheel drive applications, hydraulic couplings are used to automatically control the drive torque transferred from a driven member to a non-driven member in response to speed differentiation therebetween. In limited slip applications, such as in an axle assembly, full-time transfer case or transaxle, hydraulic couplings are used to automatically limit slip and bias the torque distribution between a pair of rotary members. Examples of hydraulic couplings which are adaptable for such driveline applications include viscous couplings, geared traction units, and electronically-controlled friction clutches generally similar to those shown and described in commonly-owned U.S. Pat. Nos. 5,148,900, 5,358,454, 5,649,459, 5,704,863 and 5,779,013.
Hydraulic couplings of the type disclosed in commonly-owned U.S. Pat. No. 5,704,863 include a clutch assembly operatively interconnected between a pair of rotary members, and a hydraulic pump for generating a fluid pumping action in response to relative rotation between the two rotary members that is used to actuate the clutch assembly. The clutch assembly includes a piston which is adapted to exert a clutch engagement force on a clutch pack operatively coupled between the two rotary members. The clutch engagement force is a function of the fluid pressure generated by the hydraulic pump. Additionally, control valving is provided for controlling the torque transfer characteristics of the hydraulic coupling. In particular, the control valving inhibits torque transfer during relatively low speed differentials between the rotary members to accommodate the tight turns required for negotiating curves or parking the motor vehicle. However, when higher speed differentials occur, the pressure generated overcomes the control valving and causes the piston to be applied to the clutch pack. Thus, such hydraulic couplings provide progressive torque transfer characteristics which vary in proportion to the relative differential speeds between the two rotary members.
While known hydraulic couplings, including but not limited to those disclosed or discussed above, have proven to be acceptable for various vehicular driveline applications, such devices are nevertheless susceptible to improvements that may enhance their performance and cost. With this in mind, a need exists to develop improved hydraulic couplings which advance the art.